Phased array system



R. F. PATTERSON, JR

; SWITCHED DELAY LINE J SWITCHED 22 3O DELAY LINE swITcHED 24 SUMMING DELAY LINE NETWORK I5 fie I SWITCHED DELAY LINE 'l m L SWITCHED DELAY LINE I IF I G. 1 BINARY 32 CONTROL PHASED ARRAY SYSTEM Filed June 1, 1964 62 A JILL L 9e 98 I00 IF IG. 3

INVENTOR.

ATTORNEY.

nited States ABSTRACT OF THE DISCLOSURE A multi-section switched delay line operative in response to binary control signals to produce selected amounts of time delay. Each of the switched delay line sections includes a first and second quadrature hybrid. Each hybrid has an input terminal, a pair of quadrature terminals, and an output terminal. A diode connects each quadrature terminal of the first hybrid to a corresponding quadrature terminal of the second hybrid. A first delay connects the output terminal of the first hybrid to an input terminal of a succeeding section and a second delay connects the output terminal of the second hybrid to another input terminal of the succeeding section. The diodes are rendered conducting in response to control signals whereby an input signal applied to the input terminal of the first hybrid is transferred to the output terminal of the second hybrid or an input signal applied to the input terminal of the second hybrid is transferred to the output terminal of the first hybrid.

This invention relates to phased array antennas and more particularly to digitally controlled beam steering systems therefor.

In a phased array antenna, the antenna beam is steered by adjusting the relative phase shifts in individual antenna element channels of the array such that coherent addition of signals received by the array occurs for signals arriving from a specified direction. These arrays are, however, inherently frequency sensitive due to the frequency dependent nature of the signal phase, and consequently, the antenna beam steering direction. To overcome the disadvantage of frequency sensitivity that is inherent in these arrays, time delay steering has evolved wherein signals propagating in each antenna element channel are time delayed by selected amounts in order to bring the signals into time coherence, and thus steer the antenna beam to a specified direction. A broadband beam steering system can, therefore, be provided by varying the time delay, rather than the phase shift, in each element channel.

Heretofore, various systems have been proposed to implement time delay steering. In one known system, a helical delay line is employed and a variable time delay provided by coupling signals off the delay line at various points on the helix. Another known scheme employs a plurality of fixed delay lines, such as coaxial cables, each having a different delay time, which are individually switched into an antenna element channel to provide a given time delay. Apparatus employing these techniques, however, suffer the disadvantages of slow switching speeds, cumbersome fabrication and unwieldy size and weight.

One solution to these problems is disclosed in co-pending application S.N. 320,426, filed Oct. 31, 1963, now US Patent No. 3,295,138 entitled Phased Array System, in which binary controlled switched delay lines are employed to appropriately delay signals in each antenna element channel. Each switched delay line comprises a plurality of fixed time delays which are variously combined to produce successive increments of delay in response to binary control signals. The switched delay line itself is comprised of switch sections, each of which has two fixed delay paths either of which can be energized by means of crystal diodes, as is more fully explained in the above-identified application. Although this technique affords a rapidly adjustable time delay beam steering system, it has a drawback in that four diodes requiring energizing power are utilized in each switch section. The energizing power requirements can be considerable in a complete beam steering system which may have hundreds of switched delay lines with a corresponding multiplicity of diodes.

In accordance with the present invention, a binary controlled switched delay line is provided which requires only two diodes per switch section thereby reducing by half the power necessary to drive the diodes.

Briefly, the invention comprises a binary controlled time delay beam steering system in which quadrature hybrids and crystal diodes are employed to direct a signal through appropriate delay paths. A pair of quadrature hybrids and a pair of crystal diodes comprise each switch section which is operative to direct a signal through a first or a second delay path in response to binary control signals.

The foregoing, together with other objects, features, and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the drawings in which:

FIG. 1 is a block diagram of a phased array antenna system in which the invention finds particular utility;

FIG. 2 is a schematic diagram of a switched delay line in accordance with the present invention; and

FIG. 3 is a schematic diagram of a four section binary switched delay line embodying the invention.

Referring to FIG. 1, there is shown a five element linear array consisting of antenna elements 10, 12, 14, 16, and 18, each having associated therewith a respective switched delay line 20, 22, 24, 26, and 28. The output of each switched delay line is connected to a summing network 30, the output E of which is a signal representative of the assembled antenna beam. Suitable biasing of each switched delay line is provided by a binary control 32, which may, for example, be a digitally programmed power supply.

The antenna array can, of course, be used equally well for both transmitting and receiving, the beam steering system being essentially the same in both instances. For simplicity of explanation, its operation will be described in the receiving mode. In operation, a signal received by each antenna element is applied to a corresponding switched delay line which introduces the appropriate time delay into each element channel, in response to a proper binary control signal produced by binary control 32, to bring the signals into time coherence. The output signal from each switched delay line is thus suitably time delayed so that coherent addition of the signals from each antenna element can be accomplished by summing network 30. In order to steer the array beam through a given angular sector, it is merely necessary to vary the interchannel time delay by suitably altering the binary control signals applied to each switched delay line.

In accordance with the present invention, binary controlled variable time delay is provided by a switched delay line, illustrated in FIG. 2, wherein a pair of quadrature hybrids are employed in conjunction with a pair of crystal diodes to direct a signal to a first or a second signal path. The quadrature hybrids, or branch line couplers as they are also known, shown generally at 34 and 36, each consist of a pair of transmission lines 38 and 40 interconnected at their center points by a branch line 42 of the same width as lines 38 and 40, and interconnected at their respective extremities by narrower branch lines 44 and 46. As is known, branch lines 42, 44 and 46 are one-quarter wavelength long at the center frequency of operation, and lines 38 and 40 are one-half wavelength long. The width of the transmission lines and branch lines are determined by well known calculations to provide the desired characteristic impedance. These hybrids, typically, are constructed of strip transmission line, although other transmission means may be employed.

The operation of these hybrids is Well known and will, therefore, be discussed only briefly here. When a signal is applied to any one of the hybrid terminals, a pair of quadrature signals will appear at the terminals opposite the input terminal. For example, referring to FIG. 2, a signal e applied to terminal 82 causes a pair of quadrature signals to appear at quadrature terminals 48 and 50. If the quadrature terminals are open circuited, the quadrature signals will be reflected back into the hybrid structure and will recombine to appear at terminal 68. It will be seen that the signal flow atforded by the quadrature hybrid can be used to provide a novel switching technique especially attractive for phased array beam steering systems.

Quadrature terminals 48 and 50 of hybrid 34 are connected respectively to terminals 52 and 54 of hybrid 36 via diodes 56 and 58, each diode having resistors 60 connected between each diode terminal and ground. These resistors, together with the diode resistance, form a filter network which tends to equalize the transmission and reflection coefficients of the diode. A load resistor R is connected between terminal 62 and ground to prevent unwanted reflections from this terminal. Terminal 64 is connected to a delay line 66, while terminal 68 is connected through a capacitor 70 to an output line 72. Isolation of the RF signal paths from the diode biasing circuit is provided by a quarter-Wave section 74, and capacitors 70 and 76. Capacitor 76 presents a high impedance to the direct current bias signal E. At RF frequencies, however, capacitor 76 oifers essentially a short circuit from point 78 to ground, this short circuit, translated through quarter-Wave section 74, presenting a high impedance at point 80. In this manner, RF energy propagating in the hybrid arms is not aifected by the biasing circuit since the latter is decoupled by the high impedance at point 80. Similarly, capacitor 70 is essentially a short circuit so that RF energy propagates unimpaired through signal path 72. However, capacitor 70 otters an open circuit to direct current thereby decoupling the biasing circuit from subsequent circuitry.

In operation, a signal e applied to input terminal 82, will appear at either terminal 68 or 64, depending upon the state of diodes 56 and 58. When diodes 56 and 58 are both rendered conducting by application of a suitable bias potential E, the input signal e divides within hybrid 34 and appears at quadrature terminals 48 and 50, propagates across the low impedance path presented by the conducting diodes and enters quadrature terminals 52 and 54 of hybrid 36 wherein the divided signal recombines and appears at output terminal 64. When diodes 56 and 58 are both non-conducting, an open circuit is presented at quadrature terminals 48 and 50; therefore, an input signal e applied to input terminal 82 is reflected from terminals 48 and 50 and appears at output terminal 68. Thus, a signal can be directed to either of two outputs by merely altering the state of diodes 56 and 58. A suit-able delay line can be connected to one or both of the output terminals, such as delay line 66 connected to terminal 64, to provide different delay paths. It can be seen that a signal e having a delay determined by the length of delay line 66, or a signal e having no delay, can be provided by appropriately biasing diodes 56 and 58.

This technique is incorporated in a practical switched delay line depicted in FIG. 3, wherein four switch sections of the type shown in FIG. 2 are employed to provide seven increments of time delay. The output of each section is connected to the input of each succeeding section. Load resistors R are connected between ground and the unused terminal of the first and last switch section to prevent signal reflections due to impedance mismatch. Signal paths 90, 92, and 94 have essentially zero time delay, While signal paths 96, 98, and have time delays in the ratio '1': 2T: 41-, respectively, where 'r is the smallest increment of time delay. It is evident that time delays from zero to 7T, in integral multiples of 1', are possible by judiciously combining the various signal paths. To provide zero delay, an input signal c is directed through signal paths 90, 92, and 94 to the output line 102. For a maximum delay of 71-, input signal e is directed through signal paths 96, 98 and 100 to output line 102. Intermediate values of delay are provided by directing the input signal through selected combinations of signal paths. RF decoupling is provided as in the delay line of FIG. 2.

The operation of each delay line section is identical to that of the delay line of FIG. 2. For example, a bias signal E applied to bias line 108, causes diodes 104 and 106 to conduct, thereby providing a low impedance path by which input signal e can traverse signal path 96. The absence of a bias signal on bias line 108 causes the input signal to traverse signal path 90. Similarly, a bias signal E E and E applied to bias lines 110, 112, and 114, respectively, causes the corresponding diodes to conduct, thereby directing the input signal through the signal paths associated with the conducting diodes while an absence of any of these bias signals will direct the input signal through the signal paths associated with the non-conducting diodes. Thus, an output signal e having zero delay is provided by the absence of bias signals; an output having a delay of 1- is produced by applying bias signals E and E to lines 108 and 110, respectively; a delay of 2-r is provided by applying bias signals E and E to respective terminals 110 and 112; and so on for the remaining values of delay. In this manner, an output signal e can be delayed by selected amounts according to the particular signal paths that are energized.

It will be noted that the bias signals applied to each section of the delay line are either present or absent, and are, therefore, binary in nature; thus, digital control techniques can be employed to provide a rapidly adjustable time delay. For example, a suitably programmed power supply can furnish the bias voltage required in any instance. The switched delay line can be incorporated in a phased array, such as illustrated in FIG. 1, to provide, in response to appropriate bias ssignals from the binary control, the requisite time delay in the several antenna element channels. An antenna beam controlled by this time delay beam steering system can, therefore, be steered by economical, extremely fast, and relatively simple switching means.

From the foregoing, it is evident that a simple, rapidly adjustable, digitally controlled, phased array beam steering system has been provided. The invention is not, of course, limited to the particular embodiments or construction illustrated and described herein, as many alternatives will occur to those skilled in the art. Accordingly, it is not intended to limit the invention to what has been particularly shown and described except as indicated in the appended claims.

What is claimed is:

1. In a phased array antenna system which includes a plurality of antenna elements and a like plurality of signal processing channels, beam-steering means comprising, a source of binary control signals, a multi-section switched delay line associated with each of said channels and operative in response to said binary control signals to produce selected amounts of time delay, each of said switched delay line sections including, first and second quadrature hybrids each having an input terminal, a pair of quadrature terminals, and an output terminal, a diode connecting each quadrature terminal of said first hybrid to a corresponding quadrature terminal of said second hybrid, first delay means connecting the output terminal of said first hybrid to one input terminal of a succeeding section, second delay means connecting the output terminal of said second hybrid to the other input terminal of said succeeding section, and means for rendering said diodes conducting in response to said binary control signals.

2. In a phased array antenna system which includes a plurality of antenna elements and a like plurality of signal processing channels, beam-steering means coinprising, a source of binary control signals, a multi-section switched delay line associated with each of said channels and operative in response to said binary control signals to produce selected amounts of time delay, each of said switched delay line sections including, first and second quadrature hybrids each having an input terminal, a pair of quadrature terminals, and an output terminal, a diode connecting each quadrature terminal of said first hybrid to a corresponding quadrature terminal of said second hybrid, means operatively connected to said diodes to equalize the transmission and reflection coefiicients of said diodes, first delay means connecting the output terminal of said first hybrid to one input terminal of a succeeding section, second delay means connecting the output terminal of said second hybrid to the other input terminal of said succeeding section, and means for rendering said diodes conducting in response to said binary control signals.

3. In a phased array antenna system which includes a plurality of antenna elements and a like plurality of signal processing channels, beam-steering means comprising, a source of binary control signals, a multi-section switched delay line associated with each of said channels and operative in respone to said binary control signals to produce selected amounts of time delay, each of said switched delay line sections including first and second quadrature hybrids each having an input terminal, a pair of quadrature terminals, and an output terminal, a diode connecting each quadrature terminal of said first hybrid to a corresponding quadrature terminal of said second hybrid, first delay means connecting the output terminal of said first hybrid to one input terminal of a succeeding section, second delay means connecting the output terminal of said second hybrid to the other input terminal of said succeeding section, and RF decoupling means operatively connected between said source of binary control signals and the output terminal of said first hvbrid whereby said diodes are rendered conducting in resnc-nse to said binary control signals.

References Cited UNITED STATES PATENTS 3,056,961 10/1962 Mitchell 343-854 3,145,383 8/1964 Nelson 343-1006 3,192,530 6/1965 Small 343-854 3,219,949 11/1965 Heeren 333-10 3,235,820 2/1966 Mahushian 333-31 3,255,450 6/1966 Butler 343- 3,274,601 9/1966 Blase 343-754 3,276,018 9/1966 Butler 343-100 3,295,134 12/1966 Lowe 343-100 3,295,138 12/1966 Nelson 343-854 HERMAN KARL SAALBACH, Prim'ary Examiner, C. BARAEF, Assistant Eqtam 'ner, 

